What to pay attention when modelling for animation?
When people say "modelling for animation", they are referring to making a mesh that deforms well. A model that is used in a single image is easy to position and make look good. A model that gets animated will get deformed and twisted in ways you probably never thought of and needs to look good in the process.

You need to consider how the model will be animated, think of the arm being lifted and swung around, think of extremes like swinging from an overhead bar or doing a high roundhouse kick, your model needs to be deformed by the armature without the shoulders or hips getting kinked and looking unnatural. Some rigs also allow a character's arms to be stretched and bent which also needs to be considered.

Often shapekeys are used to clean up a joint during animation but you still need a mesh that looks good deformed before you make a shapekey that adds a little polish for certain extreme positions.

Not sure of any tutorials that explain this in detail, I think it is more a matter of experience from watching your mesh deform and working out a topology that works for each position.

You can find many rigged models online from sites such as blender cloud or blendswap. Download some of the characters, pose them and look at how the mesh deforms. Enable wireframe display so you can see the topology as it is deformed. Compare how some look better deformed than others. Compare them to your characters.